The inverter is a logic gate to implement logic NOT in digital logic circuits. That is, the inverter can output a high voltage signal while receiving a low voltage signal, and can output a low voltage signal while receiving a high voltage signal. Generally, the inverter can be implemented by an N-type transistor and a P-type transistor coupled in series. However, due to the characteristic of high input impedance and low output impedance, the inverters are also used as signal buffers or delay elements for output signals, and can be applied to many kinds of circuits.
In prior art, when the inverter is operated with high voltages, the inverter may include more series-connected transistors to increase the overall voltage handling ability. However, in practical operations, since the cross voltages applied on the transistors may be different, some of the transistors may have to endure high cross voltages for a long time, which may cause damages to the transistors and lower the system stability.